One inductive proximity switch is known from European patent specification EP-A-0492029 B1. In this proximity switch, coil 12 is supplied with periodical transmitting current pulses. The effective signal is obtained by a suitable electronic circuit which responds to the received voltage induced in coil 12 by the decaying of the current which previously flows in the detected body due to the voltage induced therein by the transmitting current pulse.
In a development of the proximity switch known from EP-A0492029 B1, the just mentioned voltage induced in the coil is integrated over a relatively short time window in order to obtain a smoothened useful signal after suitable processing. This signal is compared to a reference voltage in order to generate an output signal which signals the presence of a detected body in the vicinity of the proximity switch if such a body is present. Such a proximity switch allows an outstanding switching distance in the detection of metallic bodies, e.g. of aluminum or steel.
The components of known proximity switches operating according to the principle described in EP-A-0492029 B1 are usually contained in a housing which consists of two or more parts. The housing generally composed at least of an elongate metallic cylinder and of a cap of a synthetic material which seals active surface 24, i.e. the exit surface of the magnetic field generated by the coil. Such a housing is inappropriate for applications where the proximity switch is exposed to shocks on the synthetic cap, to particularly aggressive environments, or to an increased ambient pressure. Such ambient conditions require a very rugged housing. In particular, it is very difficult to achieve a liquid- and gas-tight seal of the cap of the proximity switch. If a conventional proximity switch is used in the cited environments, the components of the proximity switch will be damaged quickly and a short lifetime of the latter is likely.